The original Tacoma Narrows Bridge often shows up in college engineering textbooks: “How NOT to Build a Bridge”.
What was wrong with the bridge?
Well, if a picture is worth a thousand words, what’s a 5:56 minute video worth? The original Tacoma Narrows Bridge was nicknamed “Galloping Gertie” and the video shows why. The bridge bounced like a galloping horse!
In the 1930s, despite the fact that it would become the third longest suspension bridge in the world, traffic was expected to be light, so the bridge was made only 39 feet wide, and the girders that held the bridge up from under the roadway were also thin and shallow. The people who designed the bridge believed that the steel cables would absorb wind and keep the bridge steady.
But the cables didn’t stop the wind, and then the thin, shallow girders became a problem. They were not strong enough to keep the wind from moving the bridge’s roadway. The construction workers knew the bridge had issues even before it was finished.
An engineering professor from the University of Washington in Seattle was brought in to look at the bridge. He made it an assignment for his college students. They all worked together on designing solutions. On November 2nd, 1940, they presented their ideas. One idea they had was to drill holes in the roadway to allow wind to pass through. Another idea was to add deflectors to the bridge to push the wind away from the road.
They didn’t get to try either one because the original Tacoma Narrows Bridge collapsed five days later on November 7th, 1940! Construction had only finished months before!
The original Narrows bridge, to put it simply, was just too narrow. No one was hurt when the bridge collapsed. People knew it was not safe, and were kept off in high winds.
Of course, the bridge was rebuilt. In 2007 they added a second bridge because traffic was growing. The bridge is strong and steady today. Around 100,000 cars travel over it every day, even in the wind.
When I cross the bridge I like to think about what I am crossing over. Since it settled there on November 7th, 1940, the roadway of the original bridge has been part of the ocean floor. It is now considered an artificial reef listed in the National Register of Historic Places! Someday I would like to see it with my own eyes, maybe even see a Giant Pacific Octopus.
Alice Kinerk 